1. Field
This disclosure relates to a device for analyzing a film on a surface of an electrode for a rechargeable lithium battery and a method of analyzing a film on a surface of an electrode for a rechargeable lithium battery using the same.
2. Description of the Related Art
Since portable electronic devices have been recently propagated, a rechargeable lithium battery having a high energy density and output voltage is highly required and has drawn more attention. The rechargeable lithium battery has relatively well satisfied the demands as compared to other batteries, so far.
During charging and discharging a rechargeable lithium battery, a film is provided on a surface of an electrode. In other words, an organic solvent of the electrolyte is decomposed on the interface between the electrode and the electrolyte to provide a passivation film (hereinafter referred to ‘SEI film’) or SEI (solid Electrolyte Interface) on the surface of the electrode.
Since the electrochemical characteristics of rechargeable lithium battery are significantly affected by the film formed on the surface of electrode, it is very important to accurately analyze the film condition. Conventionally, a film on a surface of an electrode for a rechargeable lithium battery is analyzed using any one of a transmission electron microscope (TEM), an atomic force microscope (AFM), and a field emission scanning electron microscope (FE-SEM).
The transmission electron microscope (TEM) provides a transmission image obtained under the high accelerating voltage condition of several hundred kiloelectron volt (keV), but pretreating and observing a sample consumes much time. The SEI film is an organic-inorganic composite layer and has an irregular shape, so the thickness measured in a local region (in several ten to several hundred nanometer scale) is difficult to estimate the thickness of entire film. In addition, pretreatment under the high accelerating voltage damages an organic material, deteriorating the reliability of the measurement.
The atomic force microscope (AFM) provides a surface image and may measure a thickness. However, the technical know-how is very specialized or highly required, and too much time is required for the analysis. In addition, a cantilever is applied in a contact mode, so the cantilever tip is worried to wear off during observing the thickness; in addition, it may not analyze the composition, and it may not be confirmed whether the SEI film is completely removed.
Also, the electric field emission scanning electron microscope (FE-SEM) usually provides a bulk low-magnified image using a high accelerating voltage (greater than or equal to 10 kV), so the definite monitoring for the surface shape is difficult.